1. Technical Field
The invention relates to an engine restart strategy.
2. Background Art
An engine start/stop system for a vehicle stops the internal combustion engine when the vehicle is stopped, and then starts the internal combustion engine when the driver requests acceleration. The engine also may be started, for example, due to loads on the electrical system or due to the catalyst temperature being low. For example, the internal combustion engine may be stopped when the vehicle stops at traffic lights or stops in a traffic jam. This approach is known as static start/stop. The stopping of the engine when the engine is not needed improves fuel economy, and reduces emissions. Although, sometimes, the engine may stay on when the vehicle is stopped because the alternator needs to run due to loads on the electrical system, or the engine may stay on for other reasons such as, for example, when the catalyst temperature is too low. In some approaches, fuel economy may be improved by 3-4% with static start/stop.
It is important that an engine start/stop system functions seamless and transparent to the driver, with minimal noise, vibration, and harshness. It is also important that when the driver requests torque at the wheels through the accelerator pedal, the time delay for starting the engine must be minimized.
In one example, the vehicle includes an internal combustion engine and a traditional automatic transmission. The engine torque is transferred to the wheels though a torque converter and then through the gearbox. The engine is started via a starter motor. The control system determines when to start and stop the engine based upon the driver's actions, the state of the vehicle and environmental conditions. The engine is started with the gearbox in the in gear state.
For the foregoing reasons, there is a continuing need for balancing the needs for a seamless engine start (minimal noise, vibration, and harshness) and for a fast engine start.